In assessing the roles of extracellular matrix and of target itssue in the regeneration of axons within the central nervous system (CNS), an acellular conduit: a stainless steel cannula, was inserted into the corpus clallosum of adult rats. The lumen of the tube was occluded by an obturator so as to prevent herniation of brain itssue into the tube during. The exterior, free and of the tube was capped with gel foam rather than tissue. One week after stereotactic placement of the cannula, the obturator was removed. At six weeks, regenerating callosal axons had entered the cannula. By 16 weeks, the regenerating core of tissue consisted of densely packed fascicles of unmyelinated axons, myelinated and myelinating axons, a few growth cones, many glial cells, degenerating myelin, and capillaries. All of these elements formed strikingly parallel columns that extended toward the dorsal surface of the brain, at about 90 Degrees from their normal, transverse course. The elongation of axons did not exceed about 1.3 mm. Thus, mature axons of te CNS can, without benefit of a pre-existing substrate, reenerate into a acellular tube for a limited distance in t he absence of target tissue. The ignoring neuronal, glial and endothelial processes are, apparently, able to produce their own substrates which are conducive to a rstricted axonal growth and remyelination.